The present invention pertains to a process for preparing a transition metal component for an olefin polymerization catalyst system. It also pertains to a catalyst system containing the said component as well as to a process for the synthesis of olefin polymers; the term "polymers" as used herein meaning both homopolymers and copolymers, in which the said catalyst system is used.
High-molecular-weight olefin polymers with low ash content are said to be prepared by polymerizing or copolymerizing olefins such as ethylene and its higher homologues, especially propene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene and 1-octene by means of Ziegler-Natta catalyst systems, which result from the association of a transition metal component with a cocatalyst most often consisting of a hydrocarbyl aluminum or hydrocarbyl magnesium compound. The transition metal component is obtained, in general, by associating a transition metal compound, especially a titanium compound such as TiCl.sub.4, TiCl.sub.3 or an alkyl titanate, with a magnesium compound, especially a compound containing MgCl.sub.2, and possibly an organic electron donor compound, and as the case may be, a porous organic or inorganic support.
A process for preparing such a transition metal component is known, which consists of first forming a reaction product, an organic magnesium-aluminum complex soluble in hydrocarbons by the reaction of a dialkyl magnesium or an alkyl magnesium halide with an alkyl aluminum or an aluminoxane compound in an inert hydrocarbon, after which the reaction product obtained is subjected to chlorination by HCl and the solid product resulting from this chlorination, which contains MgCl.sub.2, is finally treated with a transition metal component such as an alkyl titanate.
In studying the above-described reaction scheme, which leads to the transition metal component, applicants found that it would be possible to obtain better results by replacing the alkyl aluminum or aluminoxane compound reacted with the dialkyl magnesium or alkyl magnesium halide by an aluminosiloxane derivative as will be defined below to form the reaction product, an organic magnesium-aluminum-silicon complex.